From the Super Mario Wiki
A Mushroom Drop is a yellow Mushroom found in Mario & Luigi: Partners in Time. They are very similar to Nuts from the first Mario & Luigi game. When used, a Mushroom Drop recovers fifteen HP for all party members.
There are also other kinds of Mushroom Drops. Super Drops can refill 30 HP to Mario, Luigi, Baby Mario, and Baby Luigi. They look the same as a normal Mushroom Drop. Ultra Drops are also another kind of Mushroom Drop which refill 60 HP to Mario and the gang.
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